Research team from the Institute of Atmospheric Physics of the Chinese Academy of Sciences investigate air quality changes during COVID-19 outbreak in Beijing, China.
To curb the spread of the recent COVID-19 pandemic, many governments have enforced lockdowns and movement restrictions in various affect cities. Limiting the amount of activity outdoors, including the reduced number of cars on the road, it was expected that air quality would improve as a result of decrease in emissions due to human activity.
Unfortunately, this was not the case in certain megacities which are still experiencing severe air pollution even during a lockdown.
The team led by Professor Sun Yele studied six-year aerosol particle composition measurements to investigate responses of air quality to the changes in anthropogenic emissions during the COVID-19 outbreak in Beijing, China.
It was found that air pollution during the outbreak was particularly due to differences in chemical responses of primary and secondary aerosols, resulting from alterations in anthropogenic emission level.
"Primary gaseous and aerosol species responded directly to emission changes and decreased substantially by 30 to 50 percent", said Professor Sun. "However, secondary aerosol species that are formed from oxidation of gaseous precursors and accounted for more than 70 percent of particulate matter remained small changes of less than 12 percent. Therefore, fine particle pollution hasn't been improved as expected."
Despite air quality in Beijing improving in the last decade, with mass concentrations of both primary and secondary pollutants decreasing considerably, this new study proves that there is an increase in sulphur and nitrogen oxidation capacity. Thus, opposing the effects of emission reductions due to enhanced secondary formation.
The study highlights challenges in preventing secondary air pollution, especially in regions with a myriad of gaseous precursors in high concentration.
Professor Sun further emphasized the pressing need for bridging knowledge gaps of the chemical interactions between precursors and secondary aerosol under complex meteorological environments.